If the two requirements
of an electric circuit are met, then charge will flow through the external circuit. It is said
that there is a current - a flow of charge. Using the word current
in this context is to simply use it to say that something is happening
in the wires - charge is moving. Yet current is a physical quantity that
can be measured and expressed numerically. As a physical quantity, current
is the rate at which charge flows past a point on a circuit. As
depicted in the diagram below, the current in a circuit can be
determined if the quantity of charge Q passing through a cross section of a wire in a time t can be measured. The current is simply the ratio of the quantity of charge and time.
